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INA169: Non Linear output when I have higher loads.

Mohamed Nagibulla
Prodigy 80 points
Part Number: INA169

Hello,

I am having issues witih the INA169 in higher loads.

I am measuring the current to 4 different motors using 4 different INA169. The output goes to an ADC MAX11614EEE+ without any buffers.

Note: I am only showing 2 out of the 4 motor sense here, the others are exactly the same.

Currently when I only have 1 motor plugged in this is the results:

2.7A Vo= 0.197V

5.3A Vo= 0.387V

10.5A Vo= 0.769V

15.9A Vo= 1.163V

This all looks great and the Vout is what I expect. However, this changes once I have 2 or more motors connected to my circuit to the following:

2.7A Vo= 0.197V

5.3A Vo= 0.387V

10.5A Vo= 0.616V

15.9A Vo= 0.7V

As you can see it no longer becomes linear. I thought maybe I need more input capacitance because with more motors comes with more noise and more power demand. I increased the input capacitance to 0.47uF. However, that didn't change anything. 

Any Ideas what could cause this?

  • 0
    Guru 140200 points
    Hi Mohamed,

    are all motors powered by the same battery? Maybe the voltage of the battery breaks down when higher currents are drawn?

    Kai
  • 0 in reply to kai klaas69
    TI__Mastermind 25445 points
    Hello Mohamed,

    Thanks for considering to use Texas Instruments. Did you check each INA169 individually with just one motor at a time? This would help determine if there is a connection issue. What is supplying your current? As Kai noted, whether it is a battery or a power supply, you need to determine if it can supply the current you need when all 4 motors are powered up. To determine if it is a part problem or a supply problem, check the quiescent current of the INA169. It should be at most 125uA, and likely less than that if not damaged. After that I would check the voltage across your shunts. At 15.9A you should see 15.9mV. If the voltage is smaller than this and you can read it, its likely a supply issue. One further measure you could do, would be to depopulate the INA169 devices and see if the voltage across the shunt increases to the 15.9mV for your max load. If it is lower, yet again it could be your supply. Let us know when you have performed these and what you found.
  • 0 in reply to Patrick Simmons
    TI__Mastermind 25445 points
    Hello Mohamed,

    Were you able to check any of the items I mentioned above?
  • 0 in reply to Patrick Simmons
    Prodigy 80 points

    I fixed it by lowering the gain from 72.3K to 38K.